"Hybrid cloud deployments commonly use secure network connections such as VPNs or dedicated links (e.g., Direct Connect or ExpressRoute) to integrate on-premises data centers with public cloud environments."
- CSA Security Guidance v4.0 - Domain 1.1.2.3: Deployment Models
Reference:
CSA Security Guidance v4.0 - Domain 1

Platform as a Service (PaaS) provides a development and deployment environment with resources that enable users to deliver everything from simple cloud-based apps to sophisticated, cloud-enabled enterprise applications.
According to CSA Security Guidance v4.0 - Domain 1: Cloud Computing Concepts and Architectures:
"PaaS adds an additional layer of integration with application development frameworks, middleware capabilities, and functions such as databases, messaging, and queuing. These services allow developers to build applications on the platform with programming languages and tools that are supported by the stack." (CSA Security Guidance v4.0, Domain 1) This integration with app development and middleware is the key defining feature of PaaS.

Multiple independent deployments help isolate workloads, reducing the potential impact of a breach by confining it to a single deployment environment. Reference: [Security Guidance v5, Domain 7 - Infrastructure & Networking]